Solid-state and solution structures of hetero-aggregates formed between nBuLi and NCN pincer aryl lithium.
The reaction of NCNLi pincers (NCN = [2,6-(R(2)NCH(2))(2)C(6)H(3)](-), R = Me (), Et ()) with various equivalents of nBuLi in non-polar solvent results in the generation of novel mixed alkyl-aryl organolithium hetero-aggregates. The identification (variable temperature (1)H, (13)C, (7)Li and 2D NMR spectroscopy and X-ray crystallography) of multiple, equilibrating mixed-aggregates that form in these reactions has been achieved. Fluxional processes in the parent [NCNLi](2) dimeric homo-aggregates were re-evaluated and Li-N bond rupture was found to be in operation, a prerequisite towards further aggregation chemistry. The crystallized aggregates, with the formula (2).[nBuLi](2) or (2).[nBuLi](2), shows one amine arm from each NCNLi fragment stabilizing a [nBuLi](2) dimer. The core of the aggregates exhibit a roughly cubic Li(4)C(4) configuration with each aryl carbanion eta(3) coordinated to Li(3) triangular faces. Dissolution of microcrystalline powders of (2).[nBuLi](2) or (2).[nBuLi](2) regenerates the observed equilibria. Based on the NMR data, the remaining mixed aggregates are proposed to have the formula .[nBuLi](3) and .[nBuLi](3), respectively; the solution structure is again based on a Li(4)C(4) cluster. The relative concentration of the constituents in these equilibria was found to vary depending on the steric size of the amine groups. In the case of , the predominant species is the (2).[nBuLi](2) aggregate while for , the dimer (2) is favoured.
Chase
Preston A
PA
Faculty of Science, Debye Institute for Nanomaterials Science, Chemical Biology & Organic Chemistry, Utrecht University, Padualaan 8, 3584CH, Utrecht, The Netherlands.
Lutz
Martin
M
Spek
Anthony L
AL
Gossage
Robert A
RA
van Koten
Gerard
G
D000588:Amines / Q000737:chemistry; D003460:Crystallization; D019281:Dimerization; D008094:Lithium / Q000737:chemistry; D009682:Magnetic Resonance Spectroscopy; D008956:Models, Chemical; D008958:Models, Molecular; D008968:Molecular Conformation; D015394:Molecular Structure; D009584:Nitrogen / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D011208:Powders; D012996:Solutions; D014050:Toluene / Q000737:chemistry
D000588:Amines; D009942:Organometallic Compounds; D011208:Powders; D012996:Solutions; C434823:n-butyllithium; D014050:Toluene; D008094:Lithium; D009584:Nitrogen